let i = 0;
let img = ["login_bg2.jpg","login_bg3.jpg","login_bg4.jpg","login_bg5.jpg"
              ,"login_bg6.jpg","login_bg7.jpg","login_bg1.jpg"];
setInterval(()=>{
  (function(){
    let login = document.getElementById("login");
      if(i==img.length){
        i = 0;
      }
      if(i>0){
        login.style.transition = "3s";
      }
      login.style.backgroundImage = `url(../image/login_img/${img[i]})`;
      login.style.transition = "3s";
      i++;
  })();
},3500);